Magnetic displacement transducer



2 Sheets--Sheet l FI-G. 4

FIG. 2

I R. W. HOEPPEL FlG.3

Aug. 13, 1968 Filed May 16, 1965 INVENTOR.

3, 1968 R. w. HOEPPEL 3397347 MAGNET I C DI SPLACEMENT TRANSDUCER Filed May 16, 1966 2 Sheets-Sheet 2 F I G. 5

United States Patent O 3,397,347 MAGNETIC DISPLACEMENT TRANSDUCER Raymond W. Hoeppel, P.0. Box 5, Oak View, Calif. 93022 Continuation-in-part of application Ser. No. 219,602, Aug. 27, 1962. This application May 16, 1966, Ser. No. 550,370

11 Claims. (Cl. 317-123) ABSTRACT OF THE DISCLOSURE A displacement transducer for measuring movement of a nearby member comprises a magnetically biased vibrating reed relay having a capacitor to retard its vibration rate and ferromagnetic material attached to the moving member that alters the magnetic bias flux at the relay. The degree of movement is indicated by a transducer that is switched by the vibrating contacts of the relay, the vibration rate varying with the movement of the member.

This is a continuation-in-part of U.S. Patent No. 3,252,057 filed Aug. 27, 1962.

This invention relates to a displacement transducer and more particularly to a magnetically operated device for the measurement of linear or rotary displacements.

An object of this invention is to provide a simple, inexpensive device for the measurement of either a linear or rotary displacement.

Another object of this invention is to enable the measurement of displacements occurring at a distant point and to enable telemetering of such data over a considerable distance.

Another object is to provide a displacement transducer that can be separated from the moving member by a considerable air gap, which exerts very little restrictive force on the moving member, and which may -be used for measuring displacernent within sealed chambers.

The objects of this invention are accomplished by utilizing a novel type of vibrating reed switch to indicate, by either a change in f'equency or a change in power dissipation, the relative movement of a source of constant magnetic fluxwith respect to the switch, the flux source being mechanically coupled to the moving member to be measured. In another embodiment the fiux source is held stationary and the moving member is coupled to move a flux diverting mass.

In the accompanying drawing, FIGURE 1 shows the circuitry of the novel vibrating reed switch, showing three sources of magnetic fiux, any one of which may be used for controlling the vibration of the switch, and showing three readout devices, any one of which may be used for measuring the degree of displacement.

In FIGURE 2 is shown in cross section a device for measuring the depth of water in a sealed container utilizing essential Components shown in FIGURE 1.

FIGURES 3 and 5 show devices in cross section for the measurement of rotary -motion, and FIGURES 4 and 6 show side views in cross section of these devices, showing the means for coupling the rotary portion of the devices to an external rotating member.

To better understand the operation of the displacement transducer the vibrating magnetic reed switch shown in FIGURE 1 must be studied. This switch is fully described in U.S. Patent No. 3,252,057. In FIGURE 1 is shown a conventional double throw magnetic reed switch, 1, housed within solenoid 5. The switch comprises two normally open contacts, 2 and 3 and two normally closed contacts, 2 and 4. In the presence of a magnetic field, contacts 2 and 3 close and contacts 2 and 4 open.

In the circuit shown in FIGURE 1, the normally closed contacts are connected in series with solenoid 5, battery 6, ammeter A and a frequency meter, F. An essential Component of the vibrating switch system is capacitor 7, which normally is shunted across solenoid 5. A voltmeter may also be shunted across solenoid 5 to indicate the voltage across the solenoid. In operation, when the battery circuit is completed, current flowing through the solenoid sets up a magnetic field causing contacts 2. and 4 to open, whereupon current ceases to flow through the solenoid, the magnetic field collapses and the contacts again close, thus re-starting the cycle and thus setting the reeds in vibration which continues as long as current flows. Capacitor 7 reduces the v'brating rate of the reeds and stabilzes the vibration. The rate of vibration may be read directly on the frequency meter or indirectly by reading either the ammeter or the voltmeter. As the rate of vibration increases, the reading of the ammeter or the voltmeter increases proportionately and these readings are quite insensitive to appreciable fluctuatons in the voltage of the power supply.

If, while vibrating, switch 1 is approached by a constant source of magnetic fiux, such as permanent magnet 8, its rate of vibration will either be increased or decreased depending upon the polarity of magnetism induced by magnet 8 into the ferromagnetic reeds of the switch, and this in turn is related to the magnetic pole nearest the switch. The rate of vibration Will vary with the distance between the switch, 1, and magnet 8, and thus this distance may be measured by reading frequency meter, F, ammeter A or voltmeter V. Since normally open contacts, 2 and 3, also operate intermittantly when the switch is in vibration, these contacts also can be used to measure the frequency of vibration by connecting them in series with a power source and a frequency meter or an ammeter.

The Operating air gap between magnet 8 and the switch. 1, will vary with the strength of the magnet, the larger magnets Operating over a greater air gap. If it is desired to increase this air gap without increasing the size of the magnet, a second source of constant magnetic bias, such as a second magnet, 9, may be used to reinf-orce the field of magnet 8 at the switch and bias the switch, thus allowing magnet 8 to operate at a greater distance from the switch. When this is done, then the rate of change of frequency of the switch is less for a given amount of movement of magnet 8 than when magnet 8 operates closer to the switch; this is in view of the inverse square law. Thus the use of a second fiux source to bias the switch enables measurement of a greater degree of displacement for a given size movable magnet. Or magnet 9 may counteract the field of magnet 8, thus enabling magnet 8 to operate closer to the switch.

Other sources of magnetic bias may be used, such as solenoid 10 carrying current from battery 11, which is in turn regulated by variable resistor 12. It is, of course, obvious that all of these external sources of constant magnetic flux must be in flux coupling relationship with the switch in order to be eilective. All flux sources used as magnetic bias should be located in a fixed position with respect to the switch, but it is often desirable to have the bias flux manually adjustable, such -as by means of resistor 12, or by making the position of a bias magnet With respect to the switch manually adjustable, as shown in FIGURE 3.

In another embodiment, the normally open contacts of a magnetic reed switch may be used to switch the current through the solenoid, such as is shown in FIGURE 2 or FIGURE 3. In this instance it is necessary to bias the normally open switch contacts to a closed position by an external source of constant magnetic bias before vibration will begin. It is, of course, possible for the moving source of constant magnetic fiux, such as magnet 3, (FIG- UR-E 1) or magnet 28 (FIGURE 3) to act as a bias source to close the normally open contacts, and then any further movement of these magnets will produce the Operating flux to vary the frequency of vibration of the switch. The polarity of the bias field at the switch must oppose that of the solenod at the switch where the normally open contacts perform the solenod switching action.

It is desirable, but not necessary, that the vibrating switch be located within the solenod. It is only necessary that the solenod be in flux coupling relationship with the switch. Also, bias solenod 10, which is shown remotely located in FIGURE 1, may be wound concentric with solenoid 5, and in fact solenod 5 itself may be used as both an Operating solenod and as a bias pro'ducing solenod, the current for producing the bias being connected directly to the solenod and 'not passing through contacts 2 and 4.

In FIGURE 2 is'shown a linear displacement transducer employing a normally open magnetic reed switch, the transducer being used for measuring the level of liquid in a sealed cha-mber 13. Chamber 13 can be conencted to a closed vessel, or even a pressure vessel via outlets 13A and 13B. Chamber 13 should be constructed of non-ferromagnetic material. A permanent magnet, 15, is attached to fioat 14 which floats on the surface of the liquid in the container. Attached to the container is a vibrating switch system comprising magnetic reed switch 1& housed within solenod 19, which in turn is connected in series with power source 21, normally open contacts, 17 and 18, and ammeter A. The solenod is shunted by capacitor 20.

At some given level of liquid in the vessel, 13, the 'll'ux produced by magnet 15 at switch 16 will be suiicient to close contacts 17 and 18 and start vibration in the switch. At this point, the reading of the ammeter A will below. As the liquid level falls, magnet 15 approaches closer to the switch thus increasing the magnetic field `at the switch and increasing the rate of vibration of the switch, which in turn causes more current to flow through the ammeter. Thus the reading of the ani-meter will increase proportionately as the liquid level falls in the vessel. The level also may be measured by measuring the frequency of vibration of the switch or by measuring the voltage across the solenod as was previously described. Any of these readout devices may be located at a considerable distance from the fioat chamber and only a two wire transmitting conductor need be used to communicate this data. Since this is a low impedence system the wires need not be shielded.

In FIGURE 3 is shown a rotary displacement trans ducer utilizing the vibrating switch of FIGURE l as the sensing element. Here magnetic reed switch 22 is housed within solenod 26 which in turn is fastened to a non-ferromagnetc framework, 27. At the top of this framework is mounted permanent magnet 28 which in turn is fastened to shaft 29 which can be rotated in the directions shown by the arrows. Also, attached to this framework is permanent magnet 30 which can be rotated about pivot 31 with sufiicient friction between the pivot and the magnet that the magnet 'will stay in any position in which it is manually oriented. This magnet, 30, is used to bias the magnetic reed switch, 22, to a closed Operating position. 'In FIG- URE 4 is shown how magnet 28 and its attached shaft 29 is attached to a moving member, 34, by means of coupling 35. Thus any rotating movement of member 34 is communicated directly to magnet 28 to cause a corresponding rotary motion.

The position sensor operates in a manner similar to that of FIGURE 1 except that the normally open contacts, 23 `and 24, instead of the normally closed contacts, are connected in series with the solenod, 26, power source 33 and ammeter A to control the current through the solenod. capacitor 32 shunts the solenod. After biasing the contacts 23 and 24 to a closed condition by rotating magnet 30, the switch is set in vibration and the period of vibration will then vary with the rotary movement of magnet 28 as it is in turn moved by rotating member 34. As before, the reading of the ammeter correlates with the period of vibration and hence this reading correlates with the position of the rotating shaft 34. It is obvious that biasing magnet 30 is not necessarily required inasmuch -as the Operating magnet, 28, can serve to provide the necessary bias to close the contacts 23 and 24. However, bias magnet 30 does enable the Operating range of Operating magnet 28 to be shifted to different positions. Here again movement may be measured by means of a frequency meter or a voltrneter as well as with the ammeter shown.

Another embodiment of the displacement transducer is shown in FIGURES 5 and 6. Here, a magnetic reed switch, 36, is 'housed within a solenod, 39, which in turn is fastened to a non-ferromagnetic framework, 40. At the other end of this framework is attached a permanent magnet, 41, and between the magnet and the switch is rotatngly mounted, by means of axle 43, a ferromagnetic Inember which may be either of soft iron or can be a permanent magnet. A side view (FIGURE 6) shows how an external moving member, 44, is attached to axle 43 by means of coupling 45 so that when the external member whose displacement is to be measured is moved, ferromagnetic member 42 likewise moves.

The contacts, 37 and 38, of the switch are connected in series with a power source, 46, and an ammeter, A, 'as shown heretofore, with capacitor 47 shunted across the solenod. Then when member 44 moves, the ferromagnetic member 42 also moves, thus distorting the field of magnet 41 and either directing it toward the switch or diverting it from the switch. This Variation in magnetic flux at the switch causes a variation in vibration rate 'which is in turn measured 'by -a change in current flow through the ammeter.

It will be realized that the movable ferromagnetic member can be located in any position with respect to the source of permanent magnetic flux, the magnet in this instance, as long as it will vary the projected flux of the flux source at the switch. Thus the movable ferromagnetic member could operate beside the magnet or even on the side of the magnet projecting away from the switch. Also the ferromagnetic member could operate in a linear movement beside the magnet and distort the projected 'field of the magnet at the switch.

The vibrating switch displacement transducer, in any of the embodiments shown, can also be used to control other types of electromechanical devices, such as relays or motors, provided such are sensitive to the frequency of vibration of the current flowing through the vibrating switch, as were the frequency motor, ammeter and voltmeter previously shown. For instance, a conventional frequency-sensitive relay inserted in the circuit of FIGUR'E 1 in place of the ammeter, A, will perform a switching action when the frequency of vibration of the switch attains a given value. Similarly, a stepper motor thatis sensitive to the pulses produced by the vibrating switch, can be controlled `by the vibrating switch to produce a rotary motion that is proportional to the frequency of vibration of the switch.

The moving source of constant magnetic flux may move in any direction with respect to the switch as long as it produces a changing flux pattern at the switch. Also the movement of the magnet with respect to the switch need not be linearly proportional to the movement of the moving member to be measured.

Though the invention is described by means of embodiments as shown in the drawings, yet various modifications can, of course, `be made without departing from the scope of the following claims.

What is claimed is:

1. A displacement transducer comprising in combination a vibrating magnetic reed switch assembly, said assembly comprising in combination a solenod, a magnetic reed switch in flux coupling relationship with said solenoid, said switch comprising at least two ferromagnetic reed contacts, said contacts being responsive to a magnetic field, said switch controlling a current through said solenod, means to connect a power source with said switch and solenod, and capacitive means connected in circuit with said switch and solenod to stabilize the vibration of said switch; a source of constant magnetic flux in flux coupling relationship with said switch, said source 'being movable with respect to said switch; means to mechanically couple said source of flux to an external movable member so that said source of flux moves when said external member moves; and e'lectromechanical means connected in circuit with said switch for translating the frequency of vibraton of said switch into a mechanical action, the amount of such mechanical action correlating with the relative position of said external member with respect to said switch.

2. A displacement transducer according to claim 1 wherein said switch comprises two normally open and two normally closed reed contacts, said normally open contacts closing and said normally closed contacts opening in the presence of a magnetic field.

3. A displacement transducer according to claim 2 wherein the current through said solenod is controlled by normally open contacts.

4. A displacement transducer according to claim 2 wherein the current through said solenod is controlled =by said normally closed contacts.

5. A displacement transducer according to claim 1 including at least one source of constant magnetic bias in flux couplng relationship -with said switch, said source of bias being located in a fixed position with respect to said switch.

6. A displacement transducer according to claim 5 wherein said source of constant magnetic bias comprises at least one permanent magnet.

7. A displacement transducer according to claim 6 wherein said permanent magnet is manually movable.

8. A displacement transducer according to claim 5 wherein said source of constant magnetic bias comprises a bias solenod carrying a constant current.

9. A displacement transducer according to claim 8 including means to manually adjust said bias solenod.

10. A displacement transducer according to claim 1 wherein said constant source of magnetic flux comprises a permanent magnet.

11. A displacement transducer comprising in combination: a vibrating switch assembly, said assembly compris ing in combination a solenod, a magnetc reed switch in flux coupling relationship with said solenod, said switch comprising at least two ferromagnetic reed-contacts, said contacts being responsive to a magnetic field, said switch controlling a current through said solenod, means to connect a power source with said switch and solenod, and capacitive means connected in circu't with said switch and solenod to stabilze the vibration of said switch; a source of constant magnetc flux in flux coupling relationship with said switch and located in a fixed position with respect to said switch; a movable ferronagnetc member Operating within the flux pattern of said source of magnetic flux; means to mechancally couple said ferromagnetc member with an external moving member so that said ferromagnetic member moves when said external member moves; and electromechanical means connected in circuit with said switch for translating the frequency of vibration of said switch into a mechanical motion, the amount of said motion correlating with the relative position of said external member with respect to said source of flux and with respect to said switch.

References Cited UNITED STATES PATENTS 2,073,9l3 3/1937 Wigan 335- 87 X 2,550,605 4/ 1951 Schenck 335-87 X 3,227,838 1/1966 Hoeppel 335-153 3,251,961 5/1966 Wintrss 335-151 X 3,264,423 8/1966 Mejean et al. 335-153 LEE T. HIX, Primary Exam'ner.

J. A. SILVERMAN, Assistant Examner. 

